Structures and methods of manufacture for gas diffusion electrodes and electrode components

Abstract

Gas Diffusion Electrodes (GDEs) play a pivotal role in clean energy production as well as in electrochemical processes and sensors. These gas-consuming electrodes are typically designed for liquid electrolyte systems, and are commercially manufactured by hand or in a batch process. However, CDEs using the new electrolytes demand improved electrode structures. This invention pertains to GDEs and gas diffusion media with new structures for systems using membrane electrode assemblies (MEAs), and automated methods of manufacture that lend themselves to continuous mass production. Unexpected improvements in gas and vapor transport through the electrode are realized by incorporating a new dispersion process in the construction, reformulating the applied mix with solution additives, and creating a novel coating structure on a conductive web. Furthermore, combining these changes with a judicious choice in coating methodology allows one to produce these materials in a continuous, automated fashion.

Description

A gas diffusion electrode (GDE) consumes or is depolarized by a gas feed while allowing direct electronic transfer between the solid and gas phase. Together with the electrolyte, the GDE provides a path for ionic transfer, which is just as critical. GDEs are typically constructed from a conductive support, such as a metal mesh, carbon cloth, or carbon paper. This support is often called a web. The web is coated with hydrophobic wet-proofing layers, and finally, a catalytic layer is applied most commonly to one face. While the catalytic layer can consist of very fine particles of a precious metal mixed with a binder, many employ the methods similar to that in Petrow, et al., U.S. Pat. No. 4,082,699. This patent teaches the use of using finely divided carbon particles such as carbon black as the substrate for small (tens of angstroms) particles of the nobel metal. Thus called a "supported" catalyst, this methodology has shown superior performance and utilization of the catalyst in ele...

AI Technical Summary

Benefits of technology

It is a still further object of the invention to introduce a dispersion methodology that provides an unexpected increase in performance from diffusers and gas diffusion electrodes fabricated from carbon blacks preparing using this technique.

Problems solved by technology

However, the effectiveness of a mechanical method for intimately contacting the electrode to the polymer membrane electrolyte may be limited since the conducting membrane can frequently change dimensions with alterations in hydration and temperature.

This precipitation can be difficult to control due to the nature of the ion-conducting polymer membrane, the form of the metal salt, and the specific method employed to precipitate the metal.

Regardless, no information is relayed as to how this structure could be produced with economical means.

Thus, while the authors endorse the need for inexpensive manufacturing processes, they describe a batch coating design, which inherently limits product throughput.

Although suitable for limited production runs or R&D sized samples, there are several limitations to ultrasound.

First, since the energy is projected from a single source, i.e., the horn, the power is a function of the distance from the horn, and will diminish significantly as one moves away.

Second, as the action of the carbon black on the horn leads to abrasion and accelerated corrosion, the projected power spectrum emanating from the horn changes in time.

For these reasons, ultrasound may not be appropriate for production of large quantities of diffusers.

In addition, the current routine use of the sonic horn produces carbon black dispersions for coating that may be non-uniform and difficult to control for production of large batches of diffuser.

Furthermore, the current manufacturing methodology is limited in its applicability to continuously coating a web--a step believed to be crucial in producing an inexpensive product.

Images